This invention relates to arrays of DC-DC converters of the zero-current switching type.
Known arrays of zero-current switching converters (such as those described in Vinciarelli, U.S. Pat. No. 4,648,020, incorporated herein by reference) exploit the pulse by pulse energy quantization inherent in zero-current switching converters as a mechanism for power sharing by the converters in the array. In some such arrays, energy transfer cycles in one or more zero-current switching booster modules, each of which includes a zero-current switching converter, are synchronously triggered at a frequency which is controlled by a master controller. In one scheme, the master controller is part of a zero-current switching driver module, which includes both a zero-current switching converter and the master controller. An output of the driver module adjusts the operating frequency of the array so as to maintain the load voltage at a desired (setpoint) value. The zero-current switching converters in the driver and booster modules are characterized by an effective inductance (L) and a capacitance (C) which define a characteristic time scale, .pi..sqroot.(L*C), for the energy transfer cycle. If the characteristic time scales for all of the converters in the array are essentially equal, each converter module in the array will deliver an essentially constant fraction of the total power delivered to the load. Arrays of this kind permit modular power expansion while eliminating many of the drawbacks associated with alternative approaches (e.g. beat frequencies associated with arrays of unsynchronized converters; and saturated operation of converters in arrays which do not inherently share power).
The described array is comprised of two distinctly different kinds of converter modules: a driver and boosters. The driver incorporates the "intelligence" required to perform load voltage regulation and to communicate synchronizing information unidirectionally to the boosters; the boosters receive synchronizing information from, and augment the power handling capability of, the driver, but cannot, by themselves, perform load voltage regulation. This inherent asymmetry in structure and operation is apparent in the behavior of the described array under fault conditions: under these conditions, any of the booster modules can cease to deliver power without interrupting the operation of the array (provided only that the power drawn by the load does not exceed the sum of the power ratings of the remaining modules which comprise the array), whereas a failure of the driver module will compromise the operation of the entire array.
In another scheme described in U.S. Pat. No. 4,648,020, an array is formed of identical booster modules all controlled by a single phase shifting controller.